Attention with this. Dirname likes to mess with the slashes.
On Windows, Apache:
<?php
echo '$_SERVER[PHP_SELF]: ' . $_SERVER['PHP_SELF'] . '<br />';
echo 'Dirname($_SERVER[PHP_SELF]: ' . dirname($_SERVER['PHP_SELF']) . '<br>';
?>
prints out
$_SERVER[PHP_SELF]: /index.php
Dirname($_SERVER[PHP_SELF]: \